1. Field of the Invention
The present invention relates to a fluid filter and, more particularly, to a one-piece, combination anti-drainback and relief valve for a disposable, spin-on oil filter.
2. Summary of Related Art
Spin-on oil filters are well known devices often used in the oil circulation system of internal combustion engines to filter out small particulate matter which would otherwise abrade moving engine parts. These filters generally include a cylindrical outer container and an end plate enclosing a hollow, cylindrical filter element. Plural inlet ports and a central outlet port are provided in the end plate to allow oil to circulate through the filter element. The central outlet port is typically threaded for "spin-on" mounting of the filter to an engine filter mount. An annular gasket is utilized for effecting a seal between the filter and the engine mount or adapter plate on which the filter is mounted.
Such filters are also generally provided with an anti-drainback valve and pressure relief valve. The anti-drainback valve prevents the gravity induced, drainage of oil from the filter which would otherwise occur when the engine is not operating. This feature is desirable since a drained oil filter results in a momentary interruption in the circulation of oil when the engine resumes operation. A pressure relief valve is also generally utilized in this type of filter to permit oil flowing through the filter to bypass the filter element when a predetermined pressure threshold is surpassed due to the build-up of contaminants in the filter element.
In practice, the anti-drainback valve and pressure relief valve have generally consisted of separate elements, adding substantially to the manufacturing cost of the filter. Overall, it is clearly desirable that the manufacturing cost of the valve assemblies for such filters be minimized, since these filters are generally disposable.
Combined anti-drainback and relief valves have been proposed, but have generally required a plurality of elements associated with the valve to achieve the desired operation. The complexity of such valves adds significantly to the cost of both the materials and the assembly thereof, making such filters relatively expensive. A cost-effective one-piece, combination anti-drainback and relief valve which provides effective valve operation and long-term sealing properties has been heretofore unavailable.
In addition, such conventional spin-on oil filters typically include a perforated metal center tube disposed axially within a pleated paper filter element. The perforated center tube laterally supports the filter element, while allowing oil to pass from the filter element down through the center tube and out of the filter unit. In order to maintain a sufficient collapse strength, the size and number of perforations is limited, so that the center tube may in practice unduly impede the flow of oil therethrough. Additionally, a spring is generally required between the end of the filter element and the closed end of the container, to hold the filter element in position.
In view of the foregoing, replacement of the perforated metal center tube with a helical compression spring has been proposed. The use of a spring disposed axially within the filter element is advantageous in that there is a significantly greater open area for oil to flow through when compared with the conventional perforated center tube, while an even greater collapse strength is provided. However, the ends of such springs are typically sharp, and often damage the inner surface of the paper filter element.